Dispersed solution of carbon nanotubes and method of preparing the same

ABSTRACT

Provided are a dispersed solution of carbon nanotubes including carbon nanotubes, an organic solvent, a spacer, and a dispersant. The dispersed solution of the carbon nanotubes includes both the spacer reducing the van der Waals force of the carbon nanotubes and preventing the bundling of the carbon nanotubes and the dispersant maintaining the debundling and stability of the carbon nanotubes, thereby improving the dispersibility of the carbon nanotubes. The preparation method of the dispersed solution of the carbon nanotubes can easily produce a dispersed solution of carbon nanotubes without separately performing a chemical treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a graph illustrating the absorbances of dispersed solutions of carbon nanotubes prepared in Examples 1-4 of the present invention and Comparative Example 1.

FIG. 1B is a graph illustrating the normalized absorbances of the dispersed solutions of the carbon nanotubes prepared in Examples 1-4 of the present invention and Comparative Example 1.

FIG. 2A is a graph illustrating the absorbances of dispersed solutions of carbon nanotubes prepared in Example 5 of the present invention and Comparative Example 2.

FIG. 2B is a graph illustrating the absorbances of dispersed solutions of carbon nanotubes prepared in Examples 6-8 of the present invention.

FIG. 3 is a graph illustrating imaginary absorbance data defining a normalized width used in the present invention.

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention Technical Field of the Invention and Related Art prior to the Invention

The present invention relates to a dispersed solution of carbon nanotubes and a method of preparing the same. More particularly, the present invention relates to a dispersed solution of carbon nanotubes including a spacer and a dispersant, and a method of preparing the same.

Since discovery of carbon nanotubes (CNTs) by Iijima in 1991, the carbon nanotubes have attracted tremendous research interest as new materials. Carbon nanotubes are tubes made of carbon atoms arranged in a hexagonal, honeycomb-like structure, and have new physical properties due to nanometer-scale diameters.

It is known that the electrical characteristics of carbon nanotubes depend on the structure and diameter of the carbon nanotubes [Phys. Rev. B46, 1804 (1992); Phys. Rev. Lett. 68, 1579 (1992)]. That is, carbon nanotubes can behave like insulators, semiconductors, or conductors according to the structure and diameter of the carbon nanotubes. For example, if the shape or chirality of insulating, spiral carbon nanotubes is changed, motion of free electrons in the carbon nanotubes is changed. As a result, the carbon nanotubes behave like conductors due to relatively free motion of the free electrons or semiconductors due to the presence of barriers.

Carbon nanotubes have characteristics of good dynamic robustness and chemical stability, of both semiconductors and conductors, and of a small diameter, a long length, and a central hollow. Thus, carbon nanotubes are suitable as materials of flat panel displays, transistors, energy storage media, etc., and have high applicability to various nanometer-scale electronic devices.

In order for carbon nanotubes to be used in formation of conductive films or in manufacturing of various electronic devices, the carbon nanotubes must be effectively dispersed in a matrix such as a solution or a polymer. However, carbon nanotubes tend to agglomerate into bundles in a matrix due to a strong van der Waals force. Thus, carbon nanotubes are hardly soluble in water or other solvents, which makes it difficult to process the carbon nanotubes.

If carbon nanotubes agglomerate in a matrix, the intrinsic characteristics of the carbon nanotubes may be degraded, or upon formation of a thin film, thin uniformity may be lowered.

Due to the unique properties of carbon nanotubes, only use of commercially available dispersants makes it difficult to obtain a dispersed solution of carbon nanotubes which are sufficiently dispersed. Thus, various dispersion methods such as use of a new dispersant for uniformly dispersing or solubilizing carbon nanotubes in a solution or a binder have been proposed.

Korean Patent Laid-Open Publication No. 2001-102598 discloses a method of incorporating an alkyl group to carbon nanotubes using a chemical bond, Korean Patent Laid-Open Publication No. 2003-86442 discloses a method of increasing the solubility of carbon nanotubes by surrounding the carbon nanotubes with a polymer capable of physically interacting with the carbon nanotubes, and Korean Patent Laid-Open Publication No. 2005-97711 discloses a method of attaching to carbon nanotubes at least one functional group selected from the group consisting of a cyano group, an amino group, a hydroxyl group, a carboxyl group, a halide group, a nitrate group, a thiocyano group, a thiosulfuric acid group, and a vinyl group. Although these methods can partially improve the dispersibility of carbon nanotubes, a cost increase may be incurred and the physical properties of the carbon nanotubes may be lowered due to surface modification.

Korean Patent Laid-Open Publication No. 2004-103325 discloses a method of improving the dispersibility of carbon nanotubes by fluorinating the surfaces of the carbon nanotubes, Korean Patent Laid-Open Publication No. 2005-110912 discloses a method of improving the dispersibility of carbon nanotubes by sonicating a carbon nanotube-containing solution, and Japanese Patent Laid-Open Publication No. 2005-219986 discloses a dispersed solution of carbon nanotubes containing an aromatic polyamide as a dispersant. According to the above technologies, however, bundled carbon nanotubes are incompletely separated, which restricts the dispersion of carbon nanotubes.

In view of the above problems, there is still need to develop a method of improving the dispersibility of carbon nanotubes.

[Technical Goal of the Invention]

The present invention provides a dispersed solution of carbon nanotubes including a spacer and a dispersant.

The present invention also provides a method of preparing the dispersed solution of the carbon nanotubes.

[Structure and Operation of the Invention]

According to an aspect of the present invention, there is provided a dispersed solution of carbon nanotubes including:

carbon nanotubes;

an organic solvent;

a spacer; and

a dispersant.

In the dispersed solution of the carbon nanotubes, the spacer may be a substituted or unsubstituted C7-30 polycyclic aromatic hydrocarbon compound or a substituted or unsubstituted C3-30 heterocyclic aromatic compound.

In the dispersed solution of the carbon nanotubes, the C7-30 polycyclic aromatic hydrocarbon compound may be pentalene, indene, naphthalene, azulene, heptalene, biphenylene, indacene, acenaphthylene, fluorene, phenalene, phenanthrene, anthracene, fluorathene, triphenylene, pyrene, chrycene, naphthacene, picene, perylene, pentaphene, hexacene, rubicene, coronene, trinaphthylene, heptaphene, heptacene, pyranthrene, ovalene, etc.

In the dispersed solution of the carbon nanotubes, the C3-30 heterocyclic aromatic compound may be thiophene, thianthrene, phenothiarsine, furan, pyran, isobenzofuran, chromene, xanthene, phenoxatin, imidazole, pyrrole, pyrazole, isothiazole, isoxazole, pyridine, pyrazine, pyrimidine, pyradizine, pyrrolizine, indolizine, indole, indazole, purine, quinolizine, isoquinoline, phthalazine, naphthylidine, quinoxaline, quinazoline, cinnoline, pteridine, carbazole, phenantridine, acridine, perimidine, phenanthroline, phenazine, phenomercazine, phenarazine, phenophosphazine, phenotellurazine, phenoselenazine, phenotiazine, phenoxazine, isochroman, chroman, pyrrolidine, imidazolidine, pyrazolidine, piperidine, piperazine, indoline, isoindoline, morpholine, or a compound represented by Formula 1 below:

wherein CY1 is an aromatic ring;

X is oxygen or nitrogen;

k is 0 when X is oxygen and is 1 when X is nitrogen; and

R₁ is hydrogen.

In the dispersed solution of the carbon nanotubes, CY1 may be one selected from the group consisting of

In the dispersed solution of the carbon nanotubes, the compound of Formula 1 may be a compound selected from the group consisting of compounds represented by Formulae 2-7 below:

In the dispersed solution of the carbon nanotubes, the dispersant may be a compound including:

a head moiety including a substituted or unsubstitued C5-30 aromatic hydrocarbon group or a substituted or unsubstituted C3-30 heterocyclic aromatic group; and

a tail moiety including a repeat unit of at least one selected from the group consisting of an acrylate group, an ethylene oxide group, a propylene oxide group, and an alkyl group,

wherein the head moiety and the tail moiety may be connected to each other, and the molecular weight of the dispersant may be 20,000 or less, more preferably 5,000 or less.

In the dispersed solution of the carbon nanotubes, the C5-30 aromatic hydrocarbon group may be a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, a biphenylenyl group, an indacenyl group, an acenaphthylenyl group, a fluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluorathenyl group, a triphenylenyl group, a pyrenyl group, a chrycenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a rubicenyl group, a coronenyl group, a trinaphthylenyl group, a heptaphenyl group, a heptacenyl group, a pyranthrenyl group, an ovalenyl group, etc.

In the dispersed solution of the carbon nanotubes, the C3-30 heterocyclic aromatic group may be a thiophenyl group, a thianthrenyl group, a phenothiarsinyl group, a furanyl group, a pyranyl group, an isobenzofuranyl group, a chromenyl group, a xanthenyl group, a phenoxatinyl group, an imidazolyl group, a pyrrolyl group, a pyrazolyl group, an isothiazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyradizinyl group, a pyrrolizinyl group, an indolizinyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolizinyl group, an isoquinolinyl group, a phthalazinyl group, a naphthylidinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a pteridinyl group, a carbazolyl group, a phenantridinyl group, an acridinyl group, a perimidinyl group, a phenanthrolinyl group, a phenazinyl group, a phenomercazinyl group, a phenarazinyl group, a phenophosphazinyl group, a phenotellurazinyl group, a phenoselenazinyl group, a phenotiazinyl group, a phenoxazinyl group, an isochromanyl group, a chromanyl group, a pyrrolidinyl group, an imidazolidinyl group, a pyrazolidinyl group, a piperidinyl group, a piperazinyl group, an indolinyl group, an isoindolinyl group, a morpholinyl group, or a functional group represented by Formula 8 below:

wherein CY1 is an aromatic ring.

In the dispersed solution of the carbon nanotubes, the dispersant may be a compound selected from the group consisting of compounds represented by Formulae 9 through 23 below:

wherein n is 1 to 12, and m, p, q, and r are each 1 to 60.

In the dispersed solution of the carbon nanotubes, the polycyclic aromatic hydrocarbon compound, the heterocyclic aromatic compound, the aromatic hydrocarbon group, and the heterocyclic aromatic group may be substituted by —F, —Cl, —Br, —CN, —NO₂, or —OH.

In the dispersed solution of the carbon nanotubes, the organic solvent is not particularly limited, but may be hexanol, heptanol, octanol, nonanol, decanol, acetone, methylethylketone, ethylisobutylketone, methylisobutylketone, ethyleneglycol, ethyleneglycol methylether, ethyleneglycol mono-n-propylether, propyleneglycol, propyleneglycol methylether, propyleneglycol ethylether, propyleneglycol butylether, propyleneglycol propylether, dimethylformamide, dimethylacetoamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethylsulfoxide, γ-butyrolactone, methyl lactate, ethyl lactate, methyl β-methoxyisobutyrate, methyl α-hydroxyisobutyrate, aniline, N-methylaniline, hexane, terpineol, chloroform, toluene, propyleneglycol monomethylether acetate (PGMEA), chlorobenzene, dichlorobenzene, chloroform, N-methyl-2-pyrrolidone (NMP), etc.

The dispersed solution of the carbon nanotubes may include 0.001-5 wt % of the carbon nanotubes, 0.001-5 wt % of the spacer, 0.001-10 wt % of the dispersant, and balance of the organic solvent.

According to another aspect of the present invention, there is provided a method of preparing a dispersed solution of carbon nanotubes, the method including:

separating carbon nanotubes using a spacer; and

dispersing the carbon nanotubes using a dispersant.

In the preparation method of the dispersed solution of the carbon nanotubes, the separation of the carbon nanotubes using the spacer and the dispersing of the carbon nanotubes using the dispersant may be performed at the same time.

The preparation method of the dispersed solution of the carbon nanotubes may include:

adding the carbon nanotubes to a solution containing the spacer to prepare a first carbon nanotube solution;

sonicating the first carbon nanotube solution;

adding the dispersant to the sonicated first carbon nanotube solution to prepare a second carbon nanotube solution;

sonicating the second carbon nanotube solution;

centrifuging the sonicated second carbon nanotube solution; and

recovering a dispersed solution of the carbon nanotubes which are dispersed in the centrifuged second carbon nanotube solution.

The preparation method of the dispersed solution of the carbon nanotubes may include:

adding carbon nanotubes to a solution containing the spacer and the dispersant to prepare a carbon nanotube solution;

sonicating the carbon nanotube solution;

centrifuging the sonicated carbon nanotube solution; and

recovering a dispersed solution of the carbon nanotubes which are dispersed in the centrifuged carbon nanotube solution.

In the preparation method of the dispersed solution of the carbon nanotubes, the spacer may be a compound as defined above.

In the preparation method of the dispersed solution of the carbon nanotubes, the dispersant may be a compound as defined above.

Preferred embodiments of the present invention will now be described with reference to the attached drawings.

A dispersed solution of carbon nanotubes according to the present invention further includes a spacer preventing the bundling of carbon nanotubes, and thus, has improved dispersibility, unlike a conventional dispersed solution of carbon nanotubes having limited dispersibility without the use of a dispersion enhancer except a dispersant.

The present invention provides a dispersed solution of carbon nanotubes including carbon nanotubes, an organic solvent, a spacer, and a dispersant.

In a conventional dispersed solution of carbon nanotubes including no dispersion enhancer except a dispersant, separation of individual carbon nanotubes from carbon nanotube bundles may not be effectively performed. In this regard, the spacer is used in the present invention. The spacer as used herein is an aromatic compound that is easily adsorbed to surfaces of the carbon nanotubes due to a smaller molecular size than the dispersant, a similar surface structure to the carbon nanotubes, and thus, high affinity to the carbon nanotubes, and no affinity portion with the organic solvent.

Conventional dispersants serve to enhance the dispersibility of carbon nanotubes. However, in a case where carbon nanotubes are dispersed in the form of bundles, conventional dispersants cannot sufficiently separate individual carbon nanotubes from the carbon nanotube bundles. For example, a dispersant includes both a solvent affinity portion and a solvent portion in its molecule. Thus, the dispersant can be easily distributed at the interface between carbon nanotubes and a solvent, but is not easily adsorbed to surfaces of the carbon nanotubes. In this regard, in a case where an organic compound having low affinity with a solvent and high affinity with carbon nanotubes is adsorbed to surfaces of carbon nanotubes, the carbon nanotubes have irregular surfaces, and thus, a distance between the carbon nanotubes is increased, thereby reducing an interaction between the carbon nanotubes. Furthermore, the use of a dispersant molecule having a similar structure to the spacer enables to further enhance the dispersibility of the carbon nanotubes due to easy adsorption of the dispersant to the spacer.

The spacer may be a substituted or unsubstituted C7-30 polycyclic aromatic hydrocarbon compound or a substituted or unsubstituted C3-30 heterocyclic aromatic compound. The polycyclic aromatic hydrocarbon compound is a structure made up of, e.g., multiple benzene rings that are fused together. The polycyclic aromatic hydrocarbon compound has a similar surface structure to carbon nanotubes, and thus, can be easily adsorbed to the surfaces of the carbon nanotubes. Such structural characteristics are also applied to the heterocyclic aromatic compound.

The polycyclic aromatic hydrocarbon compound and the heterocyclic aromatic compound may include a wholly or partially fused ring system.

In more detail, the C7-30 polycyclic aromatic hydrocarbon compound may be, but not limited to, pentalene, indene, naphthalene, azulene, heptalene, biphenylene, indacene, acenaphthylene, fluorene, phenalene, phenanthrene, anthracene, fluorathene, triphenylene, pyrene, chrycene, naphthacene, picene, perylene, pentaphene, hexacene, rubicene, coronene, trinaphthylene, heptaphene, heptacene, pyranthrene, ovalene, etc. The C7-30 polycyclic aromatic hydrocarbon compound is not limited provided that it is a known polycyclic hydrocarbon compound having high affinity with carbon nanotubes.

The C3-30 heterocyclic aromatic compound may be, but not limited to, thiophene, thianthrene, phenothiarsine, furan, pyran, isobenzofuran, chromene, xanthene, phenoxatin, imidazole, pyrrole, pyrazole, isothiazole, isoxazole, pyridine, pyrazine, pyrimidine, pyradizine, pyrrolizine, indolizine, indole, indazole, purine, quinolizine, isoquinoline, phthalazine, naphthylidine, quinoxaline, quinazoline, cinnoline, pteridine, carbazole, phenantridine, acridine, perimidine, phenanthroline, phenazine, phenomercazine, phenarazine, phenophosphazine, phenotellurazine, phenoselenazine, phenotiazine, phenoxazine, isochroman, chroman, pyrrolidine, imidazolidine, pyrazolidine, piperidine, piperazine, indoline, isoindoline, morpholine, or a compound represented by Formula 1 below. The C3-30 heterocyclic aromatic compound is not limited provided that it is a known heterocyclic aromatic compound having high affinity with carbon nanotubes.

wherein CY1 is an aromatic ring;

X is oxygen or nitrogen;

k is 0 when X is oxygen and is 1 when X is nitrogen; and

R₁ is hydrogen.

In Formula 1 above, CY1 may be an aromatic ring selected from the following compounds, but is not limited provided that it is an aromatic ring known in the art. CY1 may be a fused aromatic ring.

The aromatic ring has a similar structure to carbon nanotubes, and thus, allows the C3-30 heterocyclic aromatic compound to have affinity with carbon nanotubes.

In more detail, the compound represented by Formula 1 may be a compound selected from the group consisting of compounds represented by Formulae 2-7 below:

In the dispersed solution of the carbon nanotubes, the dispersant may be a compound including: a head moiety including a substituted or unsubstitued C5-30 aromatic hydrocarbon group or a substituted or unsubstituted C3-30 heterocyclic aromatic group; and a tail moiety including a repeat unit of at least one selected from the group consisting of an acrylate group, an ethylene oxide group, a propylene oxide group, and an alkyl group, wherein the head moiety and the tail moiety may be connected to each other, and the molecular weight of the dispersant may be 20,000 or less, more preferably 5,000 or less.

The aromatic hydrocarbon group and the heterocyclic aromatic group may include a wholly or partially fused ring system.

In more detail, in the dispersant, the C5-30 aromatic hydrocarbon group may be a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, a biphenylenyl group, an indacenyl group, an acenaphthylenyl group, a fluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluorathenyl group, a triphenylenyl group, a pyrenyl group, a chrycenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a rubicenyl group, a coronenyl group, a trinaphthylenyl group, a heptaphenyl group, a heptacenyl group, a pyranthrenyl group, an ovalenyl group, etc.

In the dispersant, the C3-30 heterocyclic aromatic group may be a thiophenyl group, a thianthrenyl group, a phenothiarsinyl group, a furanyl group, a pyranyl group, an isobenzofuranyl group, a chromenyl group, a xanthenyl group, a phenoxatinyl group, an imidazolyl group, a pyrrolyl group, a pyrazolyl group, an isothiazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyradizinyl group, a pyrrolizinyl group, an indolizinyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolizinyl group, an isoquinolinyl group, a phthalazinyl group, a naphthylidinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a pteridinyl group, a carbazolyl group, a phenantridinyl group, an acridinyl group, a perimidinyl group, a phenanthrolinyl group, a phenazinyl group, a phenomercazinyl group, a phenarazinyl group, a phenophosphazinyl group, a phenotellurazinyl group, a phenoselenazinyl group, a phenotiazinyl group, a phenoxazinyl group, an isochromanyl group, a chromanyl group, a pyrrolidinyl group, an imidazolidinyl group, a pyrazolidinyl group, a piperidinyl group, a piperazinyl group, an indolinyl group, an isoindolinyl group, a morpholinyl group, or a functional group represented by Formula 8 below:

wherein CY1 is an aromatic ring.

In more detail, in the dispersed solution of the carbon nanotubes, the dispersant may be a compound selected from the group consisting of compounds represented by Formulae 9 through 23 below:

wherein n is 1 to 12, and m, p, q, and r are each 1 to 60.

With respect to the spacer and the dispersant contained in the dispersed solution of the carbon nanotubes, the polycyclic aromatic hydrocarbon compound, the heterocyclic aromatic compound, the aromatic hydrocarbon group, and the heterocyclic aromatic group may be substituted by —F, —Cl, —Br, —CN, —NO₂, or —OH.

The organic solvent is not particularly limited but may be hexanol, heptanol, octanol, nonanol, decanol, acetone, methylethylketone, ethylisobutylketone, methylisobutylketone, ethyleneglycol, ethyleneglycol methylether, ethyleneglycol mono-n-propylether, propyleneglycol, propyleneglycol methylether, propyleneglycol ethylether, propyleneglycol butylether, propyleneglycol propylether, dimethylformamide, dimethylacetoamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethylsulfoxide, γ-butyrolactone, methyl lactate, ethyl lactate, methyl β-methoxyisobutyrate, methyl α-hydroxyisobutyrate, aniline, N-methylaniline, hexane, terpineol, chloroform, toluene, propyleneglycol monomethylether acetate (PGMEA), chlorobenzene, dichlorobenzene, chloroform, N-methyl-2-pyrrolidone (NMP), etc.

In an embodiment of the present invention, the dispersed solution of the carbon nanotubes may include 0.001-5 wt % of the carbon nanotubes, 0.001-5 wt % of the spacer, 0.001-10 wt % of the dispersant, and balance of the organic solvent.

If the content of the carbon nanotubes is less than 0.001 wt %, the characteristics of the carbon nanotubes may not be sufficiently exhibited. On the other hand, if it exceeds 5 wt %, solvation may be limited due to a high specific surface area and a low density. If the content of the spacer is less than 0.001 wt %, the number of the spacer molecules contacting with the carbon nanotubes may be small relative to a surface area of the carbon nanotubes. On the other hand, if it exceeds 5 wt %, the solubility and characteristics of the spacer may be lowered.

The present invention also provides a method of preparing a dispersed solution of carbon nanotubes, the method including: separating carbon nanotubes using a spacer; and dispersing the carbon nanotubes using a dispersant.

In the preparation method of the dispersed solution of the carbon nanotubes, the separation of the carbon nanotubes using the spacer and the dispersing of the carbon nanotubes using the dispersant may be performed at the same time.

In more detail, in a case where the spacer and the dispersant are added in sequence, the preparation method of the dispersed solution of the carbon nanotubes may be performed as follows. That is, the carbon nanotubes are added to a solution including the spacer to prepare a first carbon nanotube solution including the carbon nanotubes and the spacer. Then, the first carbon nanotube solution is sonicated to disperse the carbon nanotubes. At this time, the spacer is adsorbed to surfaces of the carbon nanotubes. Then, the dispersant is added to the sonicated first carbon nanotube solution to prepare a second carbon nanotube solution including the carbon nanotubes, the spacer, and the dispersant. Then, the second carbon nanotube solution is sonicated to disperse the carbon nanotubes. At this time, the dispersant is adsorbed to the surfaces of the carbon nanotubes which are spaced a predetermined distance apart from each other by the spacer. The sonicated second carbon nanotube solution is centrifuged, and a dispersed solution of the carbon nanotubes which are dispersed in the centrifuged second carbon nanotube solution is recovered.

In a case where the spacer and the dispersant are added at the same time, the preparation method of the dispersed solution of the carbon nanotubes may be performed as follows. That is, the carbon nanotubes are added to a solution including the spacer and the dispersant to prepare a carbon nanotube solution including the spacer, the dispersant, and the carbon nanotubes, and the carbon nanotube solution is sonicated to disperse the carbon nanotubes. Then, the sonicated carbon nanotube solution is centrifuged, and a dispersed solution of the carbon nanotubes which are dispersed in the centrifuged carbon nanotube solution is recovered.

In the preparation method of the dispersed solution of the carbon nanotubes, the spacer may be selected from all the spacers disclosed in the specification. The dispersant may also be selected from all the dispersants disclosed in the specification.

Hereinafter, the present invention will be described more specifically with reference to the following working examples. The following working examples are for illustrative purposes and are not intended to limit the scope of the invention.

Preparation of Dispersed Solutions of Carbon Nanotubes Example 1

1 mg of perylene-3,4,9,10-tetracarboxylic dianhydride used as a spacer was dissolved in 10 ml of N-methyl-2-pyrrolidone (NMP), and 2 mg of single-walled carbon nanotubes were added thereto. The resultant solution was sonicated in a sonic bath (35 kHz, 400 W) for 4 hours so that the carbon nanotubes were dispersed. Then, a solution of 2 mg of a dispersant represented by Formula 24 below in 10 ml of NMP was added to the resultant dispersed solution. The resultant solution was sonicated in a sonic bath (35 kHz, 400 W) for 8.5 hours so that the carbon nanotubes were dispersed, and then centrifuged at 8,000 rpm for 10 minutes to obtain a dispersed solution of the carbon nanotubes.

Example 2

A dispersed solution of carbon nanotubes was prepared in the same manner as in Example 1 except using 1 mg of the dispersant of Formula 24 above.

Example 3

A dispersed solution of carbon nanotubes was prepared in the same manner as in Example 1 except using 0.5 mg of perylene-3,4,9,10-tetracarboxylic dianhydride as a spacer and 1 mg of the dispersant of Formula 24 above.

Example 4

1 mg of perylene-3,4,9,10-tetracarboxylic dianhydride used as a spacer and 1 mg of the dispersant of Formula 24 above were dissolved in 20 ml of NMP, and 2 mg of single-walled carbon nanotubes were added thereto. The resultant solution was sonicated in a sonic bath (35 kHz, 400 W) for 12.5 hours so that the carbon nanotubes were dispersed, and then centrifuged at 8,000 rpm for 10 minutes to obtain a dispersed solution of the carbon nanotubes.

Example 5

1 mg of anthraquinone used as a spacer was dissolved in 10 ml of NMP, and 2 mg of single-walled carbon nanotubes were added thereto. The resultant solution was sonicated in a sonic bath (35 kHz, 400 W) for 4 hours so that the carbon nanotubes were dispersed. Then, a solution of 2 mg of the dispersant of Formula 24 above in 10 ml of NMP was added to the resultant dispersed solution. The resultant solution was sonicated in a sonic bath (35 kHz, 400 W) for 4 hours so that the carbon nanotubes were dispersed, and then centrifuged at 8,000 rpm for 10 minutes to obtain a dispersed solution of the carbon nanotubes.

Example 6

A dispersed solution of carbon nanotubes was prepared in the same manner as in Example 5 except using 1 mg of anthraquinone as a spacer and 1 mg of poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-pheylene vinylene) as a dispersant.

Example 7

A dispersed solution of carbon nanotubes was prepared in the same manner as in Example 6 except using 0.5 mg of anthraquinone as a spacer.

Example 8

A dispersed solution of carbon nanotubes was prepared in the same manner as in Example 5 except using 1 mg of anthraquinone as a spacer and 1 mg of poly(3-hexyl thiophene) (M_(W): 2,500) as a dispersant.

Comparative Example 1

A dispersed solution of carbon nanotubes was prepared in the same manner as in Example 4 except that no spacer was used and 2 mg of the dispersant of Formula 24 above was used.

Comparative Example 2

A dispersed solution of carbon nanotubes was prepared in the same manner as in Example 5 except that no spacer was used and 2 mg of the dispersant of Formula 24 above was used.

Evaluation of Dispersion Characteristics of Dispersed Solutions of Carbon Nanotubes

Absorbances of the dispersed solutions of the carbon nanotubes prepared in Examples 1-8 and Comparative Examples 1-2 were measured using a UV-Vis-NIR spectrophotometer (Cary 5000, Absorbance mode, Scanning speed: 300 nm/min) at 200-1800 nm, and the results are presented in Table 1 below and FIGS. 1A, 1B, 1C, and 1D. Normalized widths of E₁₁ ^(S) peaks at about 1,000 nm were calculated from Equation 1 below by normalizing the absorption spectra. FIG. 1B illustrates the normalized absorption spectra of the dispersed solutions of the carbon nanotubes prepared in Examples 1-4 and Comparative Example 1.

TABLE 1 Example Normalized width Example 1 105.5 Example 2 108.7 Example 3 105.7 Example 4 98.7 Example 5 128.3 Example 6 76.2 Example 7 94.5 Example 8 119.4 Comparative Example 1 169.8 Comparative Example 2 207.5

The normalized width in Table 1 above is defined by Equation 1 below, and the width and height of a resonant band are defined in FIG. 3.

Normalized width=(width of resonant band)/(height of resonant band)  <Equation 1>

The normalized width of Equation 1 is the criteria for evaluating the degree of dispersion of a dispersed solution. As a normalized width decreases, the degree of dispersion increases.

As shown in Table 1 above, the dispersed solutions of the carbon nanotubes prepared in Examples exhibited a normalized width less than 130, whereas the dispersed solutions of the carbon nanotubes prepared in Comparative Examples exhibited a normalized width of 169 or more. That is, the degree of dispersion of the dispersed solutions of the carbon nanotubes prepared in Examples wherein both a dispersant and a spacer were used was improved relative to that of the dispersed solutions of the carbon nanotubes prepared in Comparative Examples in which no spacer was used. Such improved dispersibility of the dispersed solutions of the carbon nanotubes is attributed to the use of a spacer that is adsorbed to surfaces of carbon nanotubes and thus reduces the van der Waals force of the carbon nanotubes, thereby preventing the bundling of the carbon nanotubes, resulting in an increase in degree of dispersion of the carbon nanotubes.

Effect of the Invention

A dispersed solution of carbon nanotubes according to the present invention includes both a spacer reducing the van der Waals force of carbon nanotubes and preventing the bundling of the carbon nanotubes and a dispersant maintaining the debundling and stability of the carbon nanotubes, thereby improving the dispersibility of the carbon nanotubes. A method of preparing the dispersed solution of the carbon nanotubes according to the present invention can easily produce a dispersed solution of carbon nanotubes without separately performing a chemical treatment. 

What is claimed is:
 1. A dispersed solution of carbon nanotubes, comprising: carbon nanotubes; an organic solvent; a spacer; and a dispersant, wherein the dispersant is a compound comprising: a head moiety comprising a substituted or unsubstituted C₅ to C₃₀ aromatic hydrocarbon or a substituted or unsubstituted C₃ to C₃₀ heterocyclic aromatic group; and a tail moiety comprising a repeat unit selected from the group consisting of an acrylate group, an ethylene oxide group, a propylene oxide group, and an alkyl group, wherein the head moiety and the tail moiety are connected to each other and the molecular weight of the dispersant is less than or equal to about 20,000, wherein the dispersant is a compound represented by Formulae 9 through 21:

wherein n is 1 to 12, and m, p, q, and r are each independently 1 to 60 and, R₁₁ to R₂₀ are each independently —F, —Cl, —Br, —CN, —NO2, or —OH.
 2. The dispersed solution of claim 1, wherein the spacer is a compound selected from the group consisting of a substituted or unsubstituted C₇ to C₃₀ polycyclic aromatic hydrocarbon compound or a substituted or unsubstituted C₃ to C₃₀ heterocyclic aromatic compound.
 3. The dispersed solution of claim 2, wherein the C₇ to C₃₀ polycyclic aromatic hydrocarbon compound is a compound selected from the group consisting of pentalene, indene, naphthalene, azulene, heptalene, biphenylene, indacene, acenaphthylene, fluorene, phenalene, phenanthrene, anthracene, fluorathene, triphenylene, pyrene, chrycene, naphthacene, picene, perylene, pentaphene, hexacene, rubicene, coronene, trinaphthylene, heptaphene, heptacene, pyranthrene, and ovalene.
 4. The dispersed solution of claim 2, wherein the C₃ to C₃₀ heterocyclic aromatic compound is a compound selected from the group consisting of thiophene, thianthrene, phenothiarsine, furan, pyran, isobenzofuran, chromene, xanthene, phenoxatin, imidazole, pyrrole, pyrazole, isothiazole, isoxazole, pyridine, pyrazine, pyrimidine, pyradizine, pyrrolizine, indolizine, indole, indazole, purine, quinolizine, isoquinoline, phthalazine, naphthylidine, quinoxaline, quinazoline, cinnoline, pteridine, carbazole, phenantridine, acridine, perimidine, phenanthroline, phenazine, phenomercazine, phenarazine, phenophosphazine, phenotellurazine, phenoselenazine, phenotiazine, phenoxazine, iso chroman, chroman, pyrrolidine, imidazolidine, pyrazolidine, piperidine, piperazine, indoline, isoindoline, morpholine, and a compound represented by Formula 1 below:

wherein CY1 of Formula 1 is an aromatic ring; X is oxygen or nitrogen; k is 0 when X is oxygen and is 1 when X is nitrogen; and R₁ is hydrogen.
 5. The dispersed solution of claim 4, wherein CY1 of Formula 1 is selected from the group consisting of


6. The dispersed solution of claim 4, wherein the compound of Formula 1 is a compound selected from the group consisting of compounds represented by Formulae 2 through 7:


7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled)
 11. The dispersed solution of claim 2, wherein the polycyclic aromatic hydrocarbon compound, the heterocyclic aromatic compound, or both are independently substituted by —F, —Cl, —Br, —CN, —NO₂, or —OH.
 12. The dispersed solution of claim 7, wherein the aromatic hydrocarbon group, the heterocyclic aromatic group, or both are independently substituted by —F, —Cl, —Br, —CN, —NO₂, or —OH.
 13. The dispersed solution of claim 1, wherein the organic solvent is selected from the group consisting of hexanol, heptanol, octanol, nonanol, decanol, acetone, methylethylketone, ethylisobutylketone, methylisobutylketone, ethyleneglycol, ethyleneglycol methylether, ethyleneglycol mono-n-propylether, propyleneglycol, propyleneglycol methylether, propyleneglycol ethylether, propyleneglycol butylether, propyleneglycol propylether, dimethylformamide, dimethylacetoamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethylsulfoxide, γ-butyrolactone, methyl lactate, ethyl lactate, methyl β-methoxyisobutyrate, methyl α-hydroxyisobutyrate, aniline, N-methylaniline, hexane, terpineol, chloroform, toluene, propyleneglycol monomethylether acetate, chlorobenzene, dichlorobenzene, chloroform, and N-methyl-2-pyrrolidone, or a combination comprising at least one of the foregoing.
 14. The dispersed solution of claim 1, wherein the dispersed solution comprises about 0.001 weight percent to about 5 weight percent carbon nanotubes, about 0.001 weight percent to about 5 weight percent spacer, about 0.001 weight percent to about 10 weight percent dispersant, and a balance of a weight of the dispersed solution being the organic solvent.
 15. A method of preparing a dispersed solution of carbon nanotubes, the method comprising: inserting a spacer between carbon nanotubes; and dispersing the carbon nanotubes using a dispersant.
 16. The method of claim 15, wherein the inserting the spacer between the carbon nanotubes and dispersing the nanotubes using the dispersant are performed at the same time.
 17. The method of claim 15, wherein the spacer is a compound selected from the group consisting of a substituted or unsubstituted C₇ to C₃₀ polycyclic aromatic hydrocarbon compound or a substituted or unsubstituted C₃ to C₃₀ heterocyclic aromatic compound.
 18. The method of claim 17, wherein the C₇ to C₃₀ polycyclic aromatic hydrocarbon compound is a compound selected from the group consisting of pentalene, indene, naphthalene, azulene, heptalene, biphenylene, indacene, acenaphthylene, fluorene, phenalene, phenanthrene, anthracene, fluorathene, triphenylene, pyrene, chrycene, naphthacene, picene, perylene, pentaphene, hexacene, rubicene, coronene, trinaphthylene, heptaphene, heptacene, pyranthrene, and ovalene.
 19. The method of claim 17, wherein the C₃ to C₃₀ heterocyclic aromatic compound is a compound selected from the group consisting of thiophene, thianthrene, phenothiarsine, furan, pyran, isobenzofuran, chromene, xanthene, phenoxatin, imidazole, pyrrole, pyrazole, isothiazole, isoxazole, pyridine, pyrazine, pyrimidine, pyradizine, pyrrolizine, indolizine, indole, indazole, purine, quinolizine, isoquinoline, phthalazine, naphthylidine, quinoxaline, quinazoline, cinnoline, pteridine, carbazole, phenantridine, acridine, perimidine, phenanthroline, phenazine, phenomercazine, phenarazine, phenophosphazine, phenotellurazine, phenoselenazine, phenotiazine, phenoxazine, iso chroman, chroman, pyrrolidine, imidazolidine, pyrazolidine, piperidine, piperazine, indoline, isoindoline, morpholine, and a compound represented by Formula 1 below:

wherein CY1 of Formula 1 is an aromatic ring; X is oxygen or nitrogen; k is 0 when X is oxygen and is 1 when X is nitrogen; and R₁ is hydrogen.
 20. The method of claim 19, wherein CY1 of Formula 1 is selected from the group consisting of


21. The method of claim 19, wherein the compound of Formula 1 is a compound selected from the group consisting of compounds represented by Formulae 2 through 7:


22. The method of claim 15, wherein the dispersant is a compound comprising: a head moiety comprising a substituted or unsubstituted C₅ to C₃₀ aromatic hydrocarbon group or a substituted or unsubstituted C₃ to C₃₀ heterocyclic aromatic group; and a tail moiety comprising a repeat unit selected from the group consisting of an acrylate group, an ethylene oxide group, a propylene oxide group, and an alkyl group, wherein the head moiety and the tail moiety are connected to each other, and the molecular weight of the dispersant is less than or equal to about 20,000.
 23. The method of claim 22, wherein the C₅ to C₃₀ aromatic hydrocarbon group is selected from the group consisting of a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, a biphenylenyl group, an indacenyl group, an acenaphthylenyl group, a fluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluorathenyl group, a triphenylenyl group, a pyrenyl group, a chrycenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a rubicenyl group, a coronenyl group, a trinaphthylenyl group, a heptaphenyl group, a heptacenyl group, a pyranthrenyl group, and an ovalenyl group.
 24. The method of claim 22, wherein the C₃ to C₃₀ heterocyclic aromatic group is selected from the group consisting of a thiophenyl group, a thianthrenyl group, a phenothiarsinyl group, a furanyl group, a pyranyl group, an isobenzofuranyl group, a chromenyl group, a xanthenyl group, a phenoxatinyl group, an imidazolyl group, a pyrrolyl group, a pyrazolyl group, an isothiazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyradizinyl group, a pyrrolizinyl group, an indolizinyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolizinyl group, an isoquinolinyl group, a phthalazinyl group, a naphthylidinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a pteridinyl group, a carbazolyl group, a phenantridinyl group, an acridinyl group, a perimidinyl group, a phenanthrolinyl group, a phenazinyl group, a phenomercazinyl group, a phenarazinyl group, a phenophosphazinyl group, a phenotellurazinyl group, a phenoselenazinyl group, a phenotiazinyl group, a phenoxazinyl group, an isochromanyl group, a chromanyl group, a pyrrolidinyl group, an imidazolidinyl group, a pyrazolidinyl group, a piperidinyl group, a piperazinyl group, an indolinyl group, an isoindolinyl group, a morpholinyl group, and a functional group represented by Formula 8 below:

wherein CY1 of Formula 8 is an aromatic ring.
 25. The method of claim 22, wherein the dispersant is a compound selected from the group consisting of compounds represented by Formulae 9 through 23:

wherein n is 1 to 12, and m, p, q, and r are each independently 1 to
 60. 26. A method of preparing a dispersed solution of carbon nanotubes, the method comprising: adding carbon nanotubes to a solution containing a spacer to prepare a first carbon nanotube solution; sonicating the first carbon nanotube solution; adding a dispersant to the sonicated first carbon nanotube solution to prepare a second carbon nanotube solution; sonicating the second carbon nanotube solution; centrifuging the sonicated second carbon nanotube solution; and recovering a dispersed solution of the carbon nanotubes which are dispersed in the centrifuged second carbon nanotube solution.
 27. A method of preparing a dispersed solution of carbon nanotubes, the method comprising: adding carbon nanotubes to a solution containing a spacer and a dispersant to prepare a carbon nanotube solution; sonicating the carbon nanotube solution; centrifuging the sonicated carbon nanotube solution; and recovering a dispersed solution of the carbon nanotubes which are dispersed in the centrifuged carbon nanotube solution. 